WO2022201983A1 - Internal combustion engine control device - Google Patents

Abstract

Provided is an internal combustion engine control device capable of determining the presence or absence of deterioration of a heater unit at low cost and at a timing that is as unrestricted as possible.　An ECU (15) includes: a lookup table in which rich-side, lean-side thresholds for assessing which air-fuel ratio region a voltage value VHG from an oxygen sensor (12) corresponds to, are associated with a first scale value G1 indicating a temperature T of a sensor heater (12b); a characteristic inspecting unit (40) for inspecting which air-fuel ratio region a peak (46, 47) of the voltage VHG corresponds to; a calibrating unit (41) which, on the basis of the inspection result, derives a temperature calibration coefficient K for adjusting the first scale value G1; and a deterioration determining unit (48) which determines that the sensor heater (12b) has deteriorated if a difference between an initial value of the temperature calibration coefficient K and the most recent value thereof is greater than a deterioration determination value.

Description

Control device for internal combustion engine

The present invention relates to a control device for an internal combustion engine that has a function of determining whether or not a heater portion of a high-temperature exhaust gas oxygen sensor of the internal combustion engine has deteriorated.

Conventionally, devices that detect deterioration of heaters using resistance heating are known (see Patent Documents 1 and 2, for example). In the device of Patent Document 1, a temperature sensor and a temperature detector provided for detecting the temperature of the heater and a voltage detector for detecting the voltage applied to the heater are used to determine the actual temperature of the heater. The temperature and resistance of the heater are measured, and the temperature coefficient of resistance is derived from the measured temperature and resistance. judged to be degraded.

In the device of Patent Document 2, a sensor element that outputs an electric signal indicating a voltage corresponding to the oxygen concentration in the exhaust gas of an internal combustion engine, and a heater element that heats the sensor element to a temperature equal to or higher than the activation temperature. Deterioration of the heater element is determined for the oxygen concentration detector. This judgment is made when the temperature of the sensor element heated by one or both of the heater element and the exhaust gas has passed a predetermined time sufficient for the temperature to converge to the ambient temperature of the oxygen concentration detector, and the resistance value of the heater element and a predetermined threshold value.

WO2012/165174 JP 2019-94829 A

However, according to the device of Patent Document 1, it is necessary to provide the heater with a sensor for temperature detection in order to detect the actual temperature of the heater, which increases the cost of the device.

Further, according to the apparatus of Patent Document 2, it is not necessary to provide a sensor for detecting temperature on the heater element, but it takes a long time until the temperature of the sensor element converges to the ambient temperature (outside air temperature) of the oxygen concentration detector. For example, it is necessary to wait one night (eight hours) with the vehicle engine stopped before determining the presence or absence of deterioration. For this reason, the timing at which it is possible to determine whether or not the heater element has deteriorated is considerably limited, and it takes a long time to obtain this timing.

An object of the present invention is to provide a control device for an internal combustion engine that can determine the presence or absence of deterioration of the heater section at low cost and with as few restrictions as possible, in view of the problems of the prior art.

A control device for an internal combustion engine of the present invention includes:
A detector provided so as to be in contact with exhaust gas from an internal combustion engine having exhaust pulsation, the resistance value of which changes stepwise at an oxygen concentration in the vicinity of the stoichiometric exhaust gas, and a heater part adjacent to the detector. a high-temperature exhaust gas oxygen sensor having a pulse waveform in which a detection value obtained from the resistance value of the detection portion exhibits a pulse waveform having a crest value corresponding to the temperature of the detection portion and the exhaust pulsation;
a heater temperature reading unit that obtains the temperature of the heater unit based on the resistance value of the heater unit;
a detector temperature estimator that obtains the temperature of the detector based on the temperature of the heater;
A data map showing a plurality of excess air ratio values in association with a plurality of first scaled values for the temperature of the detection unit and a plurality of second scaled values for the detected value, and a data map showing the detected value is rich. A memory for storing a lookup table showing a rich side threshold value and a lean side threshold value for determining which air-fuel ratio region of the region, the stoichiometric region, or the lean region corresponds to the first scale value. A control device for an internal combustion engine comprising:
a characteristic inspection unit that inspects which of the air-fuel ratio regions the peak of the read wave height value corresponds to while reading the wave height value during operation of the internal combustion engine;
a calibration unit that derives a temperature calibration coefficient for correcting the first scale value and calibrating the correspondence relationship based on the result of the inspection;
A deterioration determination unit that determines that the heater unit has deteriorated when an absolute value of a difference between an initial value and a latest value of the temperature calibration coefficient is larger than a predetermined deterioration determination value. do.

In the present invention, the stoichiometric amplitude (amplitude (wave height) in stoichiometric) of the high-temperature exhaust gas oxygen sensor (eg, resistive titania oxygen sensor) changes according to the actual temperature of the detection unit, and the amplitude changes. For example, if a high-temperature exhaust gas oxygen sensor has a characteristic of a stoichiometric amplitude of 4 volts when the temperature value measured as accurately as possible when new is 600 deg C, the heater section will deteriorate due to heat ( oxidation) occurs and the resistance value of the heater portion increases, the temperature of the heater portion and the temperature T of the detection portion obtained by reading the resistance value of the heater portion appear to differ from the actual temperatures, including errors. will show different values.

For example, a high-temperature exhaust gas oxygen sensor with a heat deterioration in the heater section such that the temperature T of the heater section read by the heater temperature reading section of the control device based on the resistance value of the heater section shows the actual measurement value of 600 + 50 degC. When observed through the characteristic inspection unit, the stoichiometric amplitude characteristic of the high-temperature exhaust gas oxygen sensor changes along with the actual temperature of the detection unit, so the apparent temperature of the heater unit and the temperature of the detection unit When the value T is 650 degC, the stoichiometric amplitude is observed as 4 volts. That is, in this case, it is observed that the correspondence relationship between the apparent temperature of the heater portion and the temperature T of the detection portion and the stoichiometric amplitude is shifted by about +50 degC compared to when the heater portion is new and not thermally deteriorated. .

By checking the deviation from the default correspondence relationship of the data map as described above, the temperature T of the heater section obtained by reading the resistance value of the heater section is different from the actual temperature value of the detection section. Therefore, it is possible to accurately grasp how much temperature error is present. Further, when the temperature error is large, it can be determined that the heater section has deteriorated.

Therefore, according to the present invention, an additional temperature sensor for measuring the actual temperature of the heater section, which has been conventionally required, is provided when calibrating the temperature T of the heater section read from the resistance value of the heater section and determining deterioration. becomes unnecessary. In addition, the user does not have to wait for a long time until the timing for determining whether or not the heater element is deteriorated. Therefore, it is possible to provide a control device for an internal combustion engine that can determine the presence or absence of deterioration of the heater section at low cost and with few operational restrictions.

In the present invention, the deterioration determination unit includes a flag storage unit that stores a state flag indicating whether or not the initial value of the temperature calibration coefficient has been set, and the state flag indicates whether the initial value of the temperature calibration coefficient has not been set. , the initial value of the temperature calibration factor is set to the same value as the latest value of the temperature calibration factor, and the status flag indicates that the initial value of the temperature calibration factor has been set In some cases, changing the initial value of the temperature calibration coefficient may be prohibited.

According to this, when the status flag of the flag storage unit indicates that the initial value of the temperature calibration coefficient is not set, the initial value of the temperature calibration coefficient and the latest value of the temperature calibration coefficient are the same (the difference is zero). ). Therefore, when the initial value of the temperature calibration coefficient has not been set, the initial value of the temperature calibration coefficient can be set while preventing the determination that the heater unit has deteriorated. That is, it functions as a so-called initializer, and the initial value of the temperature calibration coefficient is set by the value of the calibrated temperature calibration coefficient.

In this case, when the deterioration determination unit determines that the initial value of the temperature calibration coefficient has been obtained properly based on the result of inspection by the characteristic inspection unit, the deterioration determination unit changes the state flag of the flag storage unit to the temperature calibration coefficient. It may be set to a value indicating that the initial value of the coefficient has been set.

According to this, the calibration in the calibration unit is not so-called one-shot learning based on instantaneous observation, but integrally performed by repeating the increase and decrease of the gradually derived temperature calibration coefficient, and the temperature When it is determined that the latest value of the calibration coefficient has reached a saturated state and the state of the heater section has been captured properly, the deterioration determination section sets the state flag of the flag storage section to ON. As a result, the deterioration determination section can set the initial value of the temperature calibration coefficient to a value with excellent reproducibility.

Alternatively, the latest value of the temperature calibration coefficient, the initial value of the temperature calibration coefficient, and the state flag may be rewritten to desired values by a command from an external terminal device.

According to this, for example, when a deteriorated high-temperature exhaust gas oxygen sensor is replaced with a new one during maintenance of an automobile in use, the OBD diagnostic machine issues a learning value reset command, and the temperature calibration coefficient and state Deterioration determination must be canceled by initializing parameters such as flags. The ECU can interface with an external terminal to provide the operational capability to do this.

In the present invention, a heater control temperature derivation unit that obtains a heater control temperature Tc by the following equation, where K is the latest value of the temperature calibration coefficient and T is the temperature of the detection unit;
Tc=T×(#1/K)
A heater heat generation control section may be provided which applies a voltage modulated in pulse width according to a difference between the temperature Tc for heater control and a predetermined target temperature Ttrg to cause the heater section to generate heat.

In the present invention, the wave height (fluctuation) of the detection value from the detection unit changes according to the actual temperature (true value) of the detection unit. When the characteristic inspection unit inspects whether or not the correspondence between the wave height and the temperature T of the detection unit obtained by reading the resistance value of the heater unit conforms to a predetermined data map, the temperature of the heater unit is adjusted to an appropriate temperature. need to control. That is, if the temperature of the heater portion is too cold or too hot, proper inspection cannot be performed.

In this regard, in the present invention, the temperature T of the detection section is multiplied by the reciprocal of the temperature calibration coefficient K to obtain the temperature Tc for heater control, and the heater section is adjusted so that the temperature Tc for heater control becomes the target temperature Ttrg. By controlling the heater to generate heat, the heater temperature can be controlled to an appropriate temperature. As a result, it is possible to appropriately perform inspection by the characteristic inspection unit, and thus to appropriately determine whether or not the heater unit is deteriorated.

In this case, the target temperature value Ttrg is not limited to a constant value, and may be set so as to vibrate in conjunction with the calibration unit. That is, the temperature calibration coefficient K can be derived by learning at multiple points while changing the temperature conditions.

1 is a schematic diagram schematically showing the configuration of main parts of an internal combustion engine including a control device (ECU) according to one embodiment of the present invention; FIG. 2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1; FIG. 3 is a flowchart showing excess ratio calculation processing for calculating an excess air ratio by an excess ratio calculation unit in the ECU of FIG. 2; FIG. 4 is a graph showing how an excess air ratio in a stoichiometric region is calculated in the process of FIG. 3. FIG. FIG. 4 is a diagram showing a graph corresponding to a lookup table for obtaining a lean side threshold value LREF and a rich side threshold value RREF and a data map for calculating an excess air ratio in the process of FIG. 3; FIG. 4 is a graph schematically showing how an excess air ratio λ calculated by the process of FIG. 3 changes; FIG. FIG. 5 is a waveform diagram showing voltage waveforms representing changes in voltage values output by a voltage calculator over time obtained while driving a vehicle equipped with an internal combustion engine. 3 is a diagram showing an example of inspection by a characteristic inspection unit and calibration by a calibration unit in the ECU of FIG. 2; FIG. FIG. 5 is a diagram showing another example of inspection by the characteristic inspection unit and calibration by the calibration unit; FIG. 5 is a diagram showing another example of inspection by the characteristic inspection unit and calibration by the calibration unit; FIG. 9 is a diagram showing still another example of inspection by the characteristic inspection unit and calibration by the calibration unit;

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the main parts of a four-cycle internal combustion engine provided with an internal combustion engine control system according to an embodiment of the present invention. This control device for an internal combustion engine has a function of performing air-fuel ratio feedback control based on the deviation between the excess air ratio obtained based on the oxygen concentration in the exhaust gas of the internal combustion engine and a target excess air ratio.

As shown in the figure, an engine body 1 of this internal combustion engine includes an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 and supplied from an air cleaner 4 to the intake port. and a throttle valve 3 that adjusts according to

The throttle valve 3 is provided with a throttle sensor 5 that detects the opening degree of the throttle valve 3 . A fuel injection valve 6 for injecting fuel is provided near the intake port of the intake pipe 2 . Fuel is pressure-fed from a fuel tank (not shown) to the fuel injection valve 6 by a fuel pump.

The intake pipe 2 is provided with an intake pressure sensor 7 that detects the intake pressure in the intake pipe 2 and an intake air temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2 . An exhaust pipe 10 connected to an exhaust port of the engine body 1 is provided with a catalyst 11 for reducing unburned components in the exhaust of the exhaust pipe 10 and an oxygen sensor 12 for detecting the oxygen concentration in the exhaust.　

A spark plug 13 connected to an ignition device 14 is fixed to the engine body 1 . When an ECU (electronic control unit) 15 as a control device issues an ignition timing command to an ignition device 14 , spark discharge occurs in a cylinder combustion chamber of the engine body 1 .　

The ECU 15 receives analog voltages indicating detection values of the throttle sensor 5, the intake pressure sensor 7, the intake air temperature sensor 8, the oxygen sensor 12, the cooling water temperature sensor 17, and the atmospheric pressure sensor 20 for detecting the atmospheric pressure. . The fuel injection valve 6 is also connected to the ECU 15 .

A signal indicating the rotation angle position of the crankshaft 18 from the crank angle sensor 19 is also input to the ECU 15 . That is, the crank angle sensor 19 has a plurality of projections arranged at intervals of a predetermined angle (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, near the outer circumference of the rotor 19a. It is magnetically or optically detected by the pickup 19b, and a pulse (crank signal) is generated from the pickup 19b each time the crankshaft 18 rotates by a predetermined angle.

Specifically, the crank angle sensor 19 outputs a signal indicating a reference angle to the ECU 15 every time the piston 9 reaches top dead center or every time the crankshaft 18 rotates 360 degrees. FIG. 2 shows the main configuration of the ECU 15. As shown in the figure, the oxygen sensor 12 which supplies the detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is an oxygen sensor in high-temperature exhaust gas, and is provided so as to be in contact with the exhaust gas of an internal combustion engine having exhaust pulsation. It has a sensor element 12a as a detection section for detecting the oxygen concentration inside, and a sensor heater 12b as a heater section for heating the sensor element 12a adjacent to the sensor element 12a.

The sensor element 12a has a resistance value that changes substantially stepwise when the oxygen concentration of the exhaust gas from the internal combustion engine is in the vicinity of the stoichiometric. It presents a pulse waveform with a crest value corresponding to . As the sensor element 12a, in this embodiment, a titania oxygen sensor, which is a resistive oxygen sensor whose resistance value changes according to the oxygen concentration, is used.

The ECU 15 includes a heater heat generation control section 22 that controls the sensor heater 12b, a temperature calculation section 23 that calculates a temperature value T indicating the temperature of the sensor element 12a, and an output signal from the sensor element 12a that indicates the oxygen concentration in the exhaust gas. and a voltage calculator 24 for converting to a voltage value VHG as a detected value.

The control of the temperature of the sensor heater 12b by the heater heat generation control unit 22 is performed by pulse width modulation (PWM) control by the ECU 15 of the amount of current I supplied to the sensor heater 12b from a power source (storage battery) (not shown). The temperature calculation unit 23 includes a heater temperature reading unit 23a that obtains the temperature of the sensor heater 12b based on the resistance value of the sensor heater 12b, and a detection unit temperature estimation unit that obtains the temperature of the sensor element 12a based on the temperature of the sensor heater 12b. 23b.

The temperature calculation unit 23 calculates the temperature value T by, for example, reading each value of the heater voltage applied to the sensor heater 12b and the energized current amount I to obtain the resistance value of the sensor heater 12b. The temperature reading section 23a obtains the temperature of the sensor heater 12b, and the detection section temperature estimating section 23b obtains the temperature T of the sensor element 12a based on the obtained temperature.

Acquisition of the temperature T by the detector temperature estimator 23b is performed by converting the temperature of the sensor heater 12b into the temperature T using table data or a calculation formula showing the correspondence relationship between the temperature T prepared in advance in the ECU 15 and the temperature of the sensor heater 12b. It is done by The calculation results of the temperature calculation unit 23 and the voltage calculation unit 24 are supplied to the substitute value calculation unit 26 of the excess ratio calculation unit 25, which will be described later.

The ECU 15 also includes a rotation speed calculation unit 27 that calculates the rotation speed NE and the angular speed NETC of the internal combustion engine based on the detection result of the crank angle sensor 19, a temperature value T from the temperature calculation unit 23, and a temperature value T from the voltage calculation unit 24. and an excess air ratio calculation unit 25 for calculating an excess air ratio λ based on the voltage value VHG and the angular velocity NETC from the rotation speed calculation unit 27 .

Further, the ECU 15 includes a target value calculating section 28 as a target value setting section for calculating an excess air ratio λcmd as a control target value based on an estimated value of the amount of oxygen stored in the catalyst 11 and the operating state of the internal combustion engine, and a rotational speed The basic injection amount calculation unit 29 calculates the basic injection amount BJ based on the rotation speed NE from the calculation unit 27 and the pressure PM in the intake pipe 2 from the intake pressure sensor 7, and the excess ratio calculation unit 25. A feedback coefficient calculation unit 30 for obtaining a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation unit 29 so as to match the excess air ratio λ with the target excess air ratio λcmd; An injection amount calculation unit 31 that calculates an injection amount Ti based on the basic injection amount BJ and operates the fuel injection valve 6 is provided.

The feedback coefficient calculation unit 30 performs PID control based on the deviation between the excess air ratio λ and the target excess air ratio λcmd to calculate the feedback coefficient k. Based on the injection amount Ti calculated by the injection amount calculator 31 based on the feedback coefficient k and the basic injection amount BJ, the fuel injection valve 6 is opened for a period of time corresponding to this. Thus, an amount of fuel is injected into the cylinder combustion chamber of the engine body 1 according to the feedback coefficient k of the PID control based on the comparison between the excess air ratio λ and the target excess air ratio λcmd.

Based on the voltage value VHG from the voltage calculation unit 24 and the temperature value T from the temperature calculation unit 23, the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for the temperature characteristics. The excess air ratio λ of the exhaust gas is calculated using the data LD. However, as will be described later, this calculation is applied when the voltage value VHG is equal to or less than the lean side threshold value LREF, and when the voltage value VHG is greater than the lean side threshold value LREF, the excess air ratio λ is obtained by another method.

The excess ratio calculation unit 25 includes a torque calculation unit 32 that calculates a torque value TQ of the internal combustion engine based on the crank angular speed NETC of the internal combustion engine, and a limit threshold setting unit 33 that sets a conversion limit threshold for the linearization conversion described above. , a storage unit 34 for storing data necessary to calculate an alternative value R of the excess air ratio λ, a data map and a lookup table to be described later, and an alternative value calculation unit 26 for calculating the alternative value R.

As conversion limit thresholds, the limit threshold setting unit 33 sets a lean side threshold LREF as a lean side conversion limit threshold and a rich side threshold RREF as a rich side conversion limit threshold for the voltage value VHG from the voltage calculation unit 24. set. However, in the titania-type sensor element 12a, when the temperature changes, the dynamic range of the output value (the minimum and maximum values in the linear region of the sensor output voltage) changes. It is necessary to change the transform limit threshold according to T.

Also referring to FIG. 5, FIG. 5 shows a first scale value G1 in the horizontal direction in FIG. In FIG. 5 corresponding to , a data map having a second scale value G2 in the vertical direction and having a plurality of numerical values of the data LD associated with the voltage value VHG and the temperature value T as coordinates is set. Moreover, each example of the lookup table corresponding to the graphs 35 and 36 for obtaining the lean side threshold value LREF and the rich side threshold value RREF is superimposed on the data map.

That is, the data map associates a plurality of excess air ratio values with a plurality of first scaled values G1 for the temperature value T and a plurality of second scaled values G2 for the voltage value VHG (detected value). is shown. The lookup table shows the correspondence between the rich side threshold value RREF and the lean side threshold value LREF for determining which air-fuel ratio region the voltage value VHG corresponds to: the rich region, the stoichiometric region, or the lean region, with the first scale value G1. They are shown in relation to each other.

By storing such a data map and a lookup table corresponding to the graphs 35 and 36 in advance in the storage unit 34 in the ECU 15, data LD obtained by linearizing the voltage value VHG using these data, The lean side threshold LREF and the rich side threshold RREF can be easily obtained and set.

Graph 35 shows points on the above data map with coordinates of voltage value VHG and temperature value T, for example, where the excess air ratio λ as the boundary between the lean region and the stoichiometric region is 1.02. It is a graph obtained by obtaining a plurality of points and connecting these points by linear interpolation. Further, the graph 36 shows, for example, the excess air ratio λ as the boundary between the stoichiometric region and the rich region is 0.98, and the voltage value VHG and the temperature value T corresponding to this value are set as coordinates on the above data map. It is a graph obtained by obtaining points and connecting each of these points by linear interpolation.

For example, from the lookup table corresponding to the graph 35, when the temperature value T from the temperature calculation unit 23 is t0, the limit threshold value setting unit 33 sets the voltage value v0 derived from the coordinate t0 as the lean region and the stoichiometric value. It can be set as a lean-side threshold value LREF for the boundary with the region. Similarly, from the lookup table corresponding to the graph 36, when the temperature value T from the temperature calculation unit 23 is t0, the voltage value v1 derived from the coordinate t0 is applied to the boundary between the stoichiometric region and the rich region. It can be set as the rich side threshold value RREF.

Further, the storage unit 34 stores, as data necessary for calculating the substitute value R, an execution time Ti1 of fuel injection by the fuel injection valve 6, a torque value TQ1 stores excess air ratio λb with respect to conversion limit threshold LREF.

When the voltage value VHG exceeds the conversion limit threshold value LREF, the substitute value calculation unit 26 calculates the substitute value R by the following equation (1) using Ti2 as the execution time of the immediately preceding fuel injection and TQ2 as the immediately preceding torque value. do.
R = ((Ti1/Ti2)/(TQ1/TQ2)) x λb (1)

Then, when the voltage value VHG exceeds the conversion limit threshold value LREF, the excess ratio calculation unit 25 substitutes the substitute value R for the exhaust air ratio instead of the excess air ratio λ as the linearized data LD. Consider the excess ratio λ.

FIG. 3 shows excess ratio (lambda) calculation processing for calculating the excess air ratio λ in the excess ratio calculation unit 25 . The control by the ECU 15 including this excess ratio calculation process is executed in synchronization with the stroke of the internal combustion engine based on the pulse signal indicating the rotation angle position of the crankshaft 18 from the crank angle sensor 19 .

When the excess ratio calculation process is started, the torque TQ of the internal combustion engine is calculated by the torque calculation unit 32 based on the crank angular speed NETC from the rotational speed calculation unit 27 in step S1.

When calculating the torque TQ, two angular velocities of the crankshaft of the internal combustion engine corresponding to each of two consecutive strokes of the internal combustion engine having intake, compression, combustion expansion, and exhaust strokes are calculated. , based on which the generated torque generated by the internal combustion engine is calculated with high accuracy (see Japanese Patent No. 6254633).

Next, in step S2, based on the temperature value T from the temperature calculation unit 23, the limit threshold value setting unit 33 uses lookup tables corresponding to the graphs 35 and 36 of FIG. Set the threshold RREF.

Next, in step S3, the voltage value VHG is obtained from the voltage calculation unit 24, the voltage value VHG is corrected by the deviation VD obtained by the voltage difference confirmation unit 43 described later, and the control voltage value (detection value) is obtained. Set VHGcon.

Next, in step S4, the above data map (FIG. 5) is scanned based on the temperature value T acquired in step S2 and the voltage value VHGcon acquired in step S3, and thus the value of the voltage value VHGcon is compared with its temperature characteristics. Data LD linearized and converted to the excess air ratio λ with compensation is obtained.

Next, in step S5, it is determined whether or not the voltage value VHGcon obtained in step S3 is smaller than the rich side threshold value RREF set in step S2. If it is determined to be smaller, the process proceeds to step S16 while setting the flag F_DETECT to zero in the following step S6, sets the value of the data LD as the excess air ratio λ value LAMBDA, and ends the excess ratio calculation process of FIG. do.

If it is determined in step S5 that the voltage value VHGcon is not smaller than the rich side threshold value RREF, then in step S7 the voltage value VHGcon acquired in step S3 is larger than the lean side threshold value LREF set in step S2. Determine whether or not

When it is determined in step S7 that the voltage value VHGcon is not large, in step S8, the voltage value lref of the lean side threshold value LREF and the voltage value rref of the rich side threshold value RREF obtained in step S2 and the voltage value lref A value of excess air ratio λ (λ=1.02 in this embodiment) as a boundary between a predetermined stoichiometric region and a lean region corresponding to and a predetermined rich region and stoichiometric region corresponding to the voltage value rref Based on the excess air ratio λ value (λ=0.98 in this embodiment) as the boundary of the oxygen sensor The excess air ratio λ is calculated as data LD obtained by linearizing the excess air ratio while compensating for the temperature characteristics of No. 12, and the process proceeds to step S9.

Also referring to FIG. 4, the excess air ratio λ as the linearized converted data LD in step S8 is obtained by presetting the excess air ratio λ as the boundary between the predetermined stoichiometric region and the lean region. A variable #LLMD (for example, 1.02), and a variable #RLMD (for example, 0.98) that can preset the excess air ratio λ as the boundary between the predetermined rich region and the stoichiometric region. If there is, it can be represented by a graph as shown in FIG. In FIG. 4, the horizontal axis in the horizontal direction of the graph is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the excess air ratio λ. Therefore, for example, when the voltage value VHG is vhg1, the value λ1 of the excess air ratio λ corresponding thereto can be calculated by the following equation (2).
λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))＋#RLMD (2)

In step S9, the execution time Ti of the last fuel injection by the fuel injection valve 6, the torque TQ calculated in step S1 are set to Ti1 and TQ1, respectively, and the excess air ratio λ related to the lean side threshold value LREF is stored in the storage unit 34 as λb. . Almost at the same time, the countdown timer value TIMER indicating the valid time of the memory is reset to its predetermined initial value #TMINT. Subsequently, the flag F_DETECT is set to 1 and the process proceeds to step S16, where the value of the data LD obtained in step S8 is set as the air ratio excess ratio λ value LAMBDA, and the excess ratio calculation process of FIG. 3 ends.

At this time, the value of the data LD obtained in step S8 is stored as λb. At that time, it is preferable to store the moving average of the values of the data LD as λb. For example, the exponential moving average λa of the excess air ratio λ (data LD) obtained by the following equation (3) is stored as λb.
λa=LD×k1+λab×(1−k1) (3)

Here, k1 is the moving average coefficient, and λab is the moving average value in the previous control cycle stored in the storage unit 34. For example, 0.34 is used as the moving average coefficient k1.

Further, at this time, the storage unit 34 preferably stores moving average values as the fuel injection execution time Ti1 and the torque value TQ1. For example, the exponential moving average TiFLT of the fuel injection execution time Ti is obtained by the following equation (4) and stored as Ti1, and the exponential moving average TQFLT of the torque value TQ is obtained by the following equation (5) and TQ1 is stored as
TiFLT=Ti×k2+TiFLTb×(1−k2) (4)
TQFLT=TQ×k3+TQFLTb×(1−k3) (5)

Here, k2 and k3 are moving average coefficients, and TiFLTb and TQFLTb are moving average values stored in the storage unit 34 in the previous control cycle. In this embodiment, different values can be used for moving average coefficients k1, k2, and k3.

Next, when it is determined in step S7 that the voltage value VHGcon acquired in step S3 is larger than the lean side threshold value LREF, in step S10, it is determined whether or not the countdown timer value TIMER has reached zero. judge. Then, if TIMER has reached zero, the flag F_DETECT is reset to 0 (step S11).

Next, the process proceeds to step S12 to determine whether the flag F_DETECT=1. If F_DETECT=1, it indicates that the storage unit 34 stores the excess air ratio λb related to the lean side threshold value LREF, the fuel injection execution time Ti1, and the torque value TQ1. In the value calculator 26, the substitute value R is calculated by the above equation (1), and the value of the data LD is set as the substitute value R.

Next, in step S14, it is determined whether or not the value of data LD set in step S13 is greater than a predetermined upper limit #LLMT. If the value of the data LD set in step S13 is greater than the upper limit #LLMT, the value of the data LD is set to the upper limit #LLMT (step S15). In this case, 1.25, for example, can be used as the upper limit #LLMT.

In step S12, if F_DETECT=0, the storage unit 34 does not store valid values for the excess air ratio λb, the fuel injection execution time Ti1, and the torque value TQ1 for the lean side threshold value LREF. Therefore, the substitute value R cannot be calculated. Also in this case, the value of the data LD is set to the upper limit value #LLMT (step S15).

Therefore, the value of the data LD set in step S13 or step S15 is set as the excess air ratio λ value LAMBDA (step S16), thereby ending the excess ratio calculation process of FIG.

When the excess ratio calculation process of FIG. 3 ends, the ECU 15 converts the excess air ratio λ value LAMBDA calculated in the excess ratio calculation process of FIG. The amount of fuel injected by the fuel injection valve 6 is controlled by the PID control of the feedback coefficient calculator 30 so as to match the rate λcmd.

FIG. 6 is a graph schematically showing how the excess air ratio λ value LAMBDA calculated by the excess ratio calculation process of FIG. 3 changes. The horizontal axis of the graph is numerical values indicating the passage of time, and the vertical axis is the excess air ratio λ.

Graph 37 in FIG. 6 gradually increases the actual exhaust air excess ratio λ at a constant change rate in the range from the left end side to the vicinity of the center of the horizontal axis in the left-right direction in FIG. In the range from near the center of the horizontal axis to the right end, when the actual excess air ratio λ of the exhaust gas is gradually decreased at a constant rate of change, the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is calculated. 3 shows the numerical change in the excess air factor λ value when the excess air factor λ value is calculated using the data obtained by directly linearizing the excess air factor λ while compensating for the temperature characteristic.

Similarly, the graph 38 shows that the voltage value VHG from the voltage calculation unit 24 is lean when the actual exhaust air excess ratio λ is gradually increased or decreased at a constant change rate from the left end to the right end of the horizontal axis. When the voltage value lref of the threshold value LREF is equal to or less than the voltage value lref, the excess air ratio λ value is calculated using the data obtained by directly linearizing the voltage value VHG using the data map (FIG. 5) or formula (2) described above. However, when the voltage value VHG from the voltage calculation unit 24 exceeds the voltage value lref (corresponding to the excess air ratio λ of 1.020) of the lean threshold value LREF, the voltage value VHG is linearized. When the alternative value R obtained by the above formula (1) instead of the converted data is used as the value of the excess air ratio λ, the change in the value of the excess air ratio λ is shown.

Thus, when the actual exhaust air excess ratio λ is 1.020 or less, the voltage value VHG from the voltage calculator 24 responding thereto is proportional to the actual exhaust air excess ratio λ ( linear), when the actual exhaust air excess ratio λ is 1.020 or less, both the graphs 37 and 38 follow the constant change in the actual exhaust air excess ratio λ. However, when the excess air ratio λ of the exhaust gas exceeds 1.020, the voltage value VHG exhibiting nonlinearity under that situation rapidly changes in an increasing direction. A graph 37 showing the excess air ratio λ value based on the data obtained by directly linearizing conversion of also sharply and nonlinearly changes in the increasing direction. On the other hand, in graph 38, even when the excess air ratio λ of the exhaust exceeds 1.020 (#LLMD above), the excess air ratio λ value LAMBDA changes linearly with respect to the excess air ratio λ (air-fuel ratio) of the exhaust. , and is interlocked with the actual exhaust air excess ratio λ.

Therefore, when the voltage value VHG is equal to or less than the lean side threshold value LREF by the excess ratio calculation process, the excess air ratio λ is calculated using the above linearized converted data, and the voltage value VHG exceeds the lean side threshold value LREF. In this case, by calculating the excess air ratio λ (graph 38) using the above-described formula (1), the excess air ratio calculation unit 25 interlocks with the actual excess air ratio λ of the exhaust over the entire range of the graph in FIG. It can be seen that the proportionally changing excess air ratio λ value can be supplied to the feedback coefficient calculator 30 . As a result, interruption of the PID control by the feedback coefficient calculator 30 is suppressed.

By the way, if the resistance values of the sensor element 12a (detection section) and the sensor heater 12b (heater section) vary due to manufacturing tolerances, etc., the excess air ratio obtained based on these resistance values will also be inaccurate, resulting in air-fuel ratio feedback. There is a risk of interfering with control.

Therefore, the excess ratio calculation unit 25 includes a characteristic inspection unit 40 that inspects the characteristics of the voltage value VHG (detected value) that changes according to the variation in the resistance value, and the data map and lookup unit 40 based on the inspection result. and a calibrating unit 41 for calibrating the up-table.

The characteristic inspection unit 40 includes a temperature difference confirmation unit 42 that confirms the deviation amount TD of the temperature T from the reference value and sets the temperature Tcon for control, and an average value VHGSTD of the voltage value VHG of the sensor element 12a within a predetermined time. and a voltage difference confirmation unit 43 that confirms the deviation VD between the lean side threshold value LREF and sets the control voltage value (detected value) VHGcon, and the set control temperature Tcon and the control voltage value ( The output characteristic of the oxygen sensor 12 connected to the ECU 15 is checked according to the detected value (VHGcon).

The temperature difference confirmation unit 42 determines the amount of deviation of the temperature T from the reference value when a predetermined time has elapsed for the temperature T of the sensor element 12a to converge to the ambient temperature of the sensor element 12a while the internal combustion engine is stopped. Get a TD. Then, the temperature difference confirmation unit 42 corrects the temperature T of the sensor element 12a based on the deviation amount TD as a temperature for control used in the inspection of the characteristics of the voltage value VHG and the excess ratio calculation unit 25 (this In the embodiment, Tcon=T+TD) is set.

The reference value Tref for setting the temperature Tcon is, for example, obtained by adding the intake air temperature obtained by the intake air temperature sensor 8 to the engine temperature obtained by the cooling water temperature sensor 17 and dividing by 2 {Tref = (engine temperature + intake air temperature temperature)÷2}. As a result, the influence of quantization errors in the readings of the cooling water temperature sensor 17 and the intake air temperature sensor 8 can be reduced, and the control temperature Tcon can be set with high accuracy.

In this case, the temperature Tcon for control is set to be the same as the engine temperature and intake air temperature at room temperature and before starting. Thus, the temperature difference confirming unit 42 substantially translates the lookup table corresponding to the data map and the graphs 35 and 36 in the horizontal direction (direction of the first scale value G1) in FIG. .

Subsequently, when the control temperature Tcon of the sensor element 12a is equal to or lower than a predetermined value (e.g., equal to the reference value Tref), the voltage difference confirmation unit 43 determines the voltage value VHG obtained from the resistance value of the sensor element 12a. A deviation VD between the average value VHGSTD and the lean-side threshold value LREF within a predetermined time is obtained. Then, the voltage difference confirmation unit 43 corrects the voltage value VHG obtained from the resistance value based on the deviation VD as a voltage value (detection value) for control used in the above-described characteristic inspection and excess ratio calculation unit 25. Set the value VHGcon (=VHG+VD).

In this case, when the temperature Tcon of the sensor element 12a is sufficiently low and the oxygen sensor 12 is inactive, the wave height of the voltage value VHG becomes almost zero (a state in which the voltage value VHG does not move) and the standard resistance value has the same value as the graphs 35 and 36 (the voltage value VHGref and the graphs 35 and 36 overlap).

That is, when the temperature Tcon for control is equal to or lower than the predetermined value, the standard voltage value VHGref becomes equal to the graph 35 (lean side threshold value LREF). The value can be obtained by scanning the lookup table corresponding to graph 35 at the sufficiently low temperature Tcon.

Further, the average value VHGSTD can be obtained, for example, from the arithmetic average value of the voltage values VHG read many times in a period of 5 seconds, thereby reducing the influence of quantization errors in reading the voltage values VHG. , the deviation VD can be obtained, and the voltage value VHGcon for control can be set with high accuracy.

Thus, the control voltage value (detected value) VHGcon is corrected to be the same as the graph 35 (lean side threshold value LREF) when the control temperature Tcon is equal to or lower than the predetermined value. As a result, the voltage difference confirming unit 43 substantially translates the data map in the vertical direction (direction of the second scale value G2) in FIG.

When inspecting the oxygen sensor 12 actually connected to the ECU 15, the characteristic inspection unit 40 sets the target excess air ratio λcmd to the vicinity of the stoichiometric value through the target value calculation unit 28, acquires the peak value of the voltage value VHGcon, It is checked whether this peak value corresponds to any of the air-fuel ratio regions.

In addition, when calibrating by the calibrating unit 41, the lookup tables corresponding to the data map and the graphs 35 and 36 are calibrated based on the result of the inspection.

FIG. 7 shows the voltage obtained while driving the vehicle equipped with the oxygen sensor 12 having a standard resistance value in the internal combustion engine with the target excess air ratio λcmd set to the vicinity of the stoichiometric by the characteristic inspection unit 40. A voltage waveform 44 representing a change over time is shown for the value (detected value) VHGref. FIG. 7 also shows an air-fuel ratio waveform 45 representing the waveform of the output signal of a wideband air-fuel ratio sensor provided temporarily for verification purposes.

In a four-cycle internal combustion engine, the exhaust gas in the exhaust pipe and the oxygen concentration contained in the exhaust gas are pulsating, so as shown in FIG. The voltage waveform 44 of the voltage value (detected value) VHGref and the air-fuel ratio waveform 45 of the air-fuel ratio sensor provided side by side are observed as waveforms having wave heights that oscillate with the passage of time. During the illustrated period P in which the fuel ratio waveform 45 straddles the level at which the excess air ratio λ is 1.0, the resistance value of the sensor element 12a originally changes steeply in a stepwise manner at the oxygen concentration near the stoichiometric. , the wave height M of the voltage waveform 44 (peak value of the detected value) is observed as a waveform that oscillates much more than the wave height of the air-fuel ratio waveform 45 in the same period P. Lookup tables corresponding to the graph 36 (rich side threshold value RREF) and the graph 35 (lean side threshold value LREF) are respectively set so as to follow the wave height transition of the voltage waveform 44 that oscillates greatly. there is

That is, in the illustrated period P, among peaks of each wave height M in the voltage waveform 44 obtained from the oxygen sensor 12 having a standard resistance value, the rich peak near the lower rich threshold RREF in FIG. Many of 46 are located approximately on the rich side threshold RREF, while many of the lean peaks 47 near the upper lean side threshold LREF in FIG. 7 are located approximately on the lean side threshold LREF.

In other words, the voltage value of the oxygen sensor 12 actually connected to the ECU 15 is set while performing feedback control of the air-fuel ratio so as to reproduce the state of the illustrated period P by setting the target excess air ratio λcmd near the stoichiometric. (Detected value) The wave height M expressed by VHGcon is measured by the ECU 15, and the peak of the wave height M is checked to see if it matches the lean side threshold value LREF and the rich side threshold value RREF. It is possible to grasp and acquire how much the characteristic deviation of the voltage value VHGcon from the characteristic of the voltage value VHGref at a constant resistance value is.

Thus, the characteristic inspection unit 40 sets the target excess air ratio λcmd to the vicinity of the stoichiometric and performs the air-fuel ratio feedback control while checking the wave height of the voltage value (detection value) VHGcon of the oxygen sensor 12 connected to the ECU 15. It is configured to obtain a peak value of M and check whether the peak value of the wave height M falls within a rich region, a stoichiometric region, or a lean region. Further, based on this inspection result, the calibration unit 41 performs affine transformation so that the peak value of the wave height M conforms to the rich side threshold value RREF and the lean side threshold value LREF, and performs the data map and the lookup table. can be calibrated.

Specifically, the calibration unit 41 expands or contracts the plurality of first scale values G1 and the plurality of second scale values G2 in the manner of so-called affine transformation, thereby calibrating the data map and the lookup table. A first calibrated magnification value C1 and a second calibrated magnification value C2 are provided.

8A to 8D, the calibration unit 41 calculates the lean side peak value 47v of the control voltage value VHGcon that changes over time and the graph 35 (lean side threshold value LREF). , for example, if the lean-side peak value 47v is in the lean region, the first calibration magnification value C1 is increased, and the data map and lookup table are shifted to the right side in FIG. 8A. When the lean side peak value 47v is in the stoichiometric region, the first calibrated magnification value C1 is decreased to shrink the data map and lookup table leftward in FIG. 8B.

That is, the calibrating unit 41 multiplies the first scale value G1 of the data map and lookup table by the increased or decreased first calibration magnification value C1, so that the data map and lookup table are substantially converted in the manner of so-called affine transformation. Calibrate by expanding or contracting. Note that 0 Kelvin (minus 273.15 degC; absolute zero) can be adopted as the origin of scaling of the first scale value G1. At this time, when the values before calibration of the plurality of first scale values G1 stored in the storage unit 34 are Tk (degrees Celsius), the first scale value for control after calibration Tkcal is given by the following equation (6a): required by
Tkcal = (Tk + 273.15) x C1 - 273.15 (6a)

Further, when the calibration unit 41 compares the rich-side peak value 46v of the control voltage value VHGcon that changes over time with the lookup table corresponding to the graph 36 (rich-side threshold value RREF), For example, when the rich side peak value 46v is in the rich region, the second calibration magnification value C2 is increased to expand the data map and lookup table downward in FIG. is in the stoichiometric region, the second calibrated scale factor value C2 is decreased to shrink the data map and lookup table upward in FIG. 8C.

That is, the calibrating unit 41 multiplies the second scale value G2 of the data map and lookup table by the increased or decreased second calibration magnification value C2, so that the data map and lookup table are substantially converted in the manner of so-called affine transformation. calibrate by expanding or contracting It should be noted that the value of the graph 35 (lean-side threshold value LREF) when the above-described control temperature Tcon is equal to or lower than a predetermined value can be adopted as the scaling origin of the second scale value G2.

At this time, when the value of the graph 35 when the control temperature Tcon is equal to or lower than a predetermined value is LREFanchor, and the values before calibration of the plurality of second scale values G2 stored in the storage unit 34 are Vk, the calibration The subsequent control second scale value Vkcal is obtained by the following equation (7).
Vkcal=(Vk-LREFanchor)×C2+LREFanchor (7)

In the present embodiment, when the first calibrated magnification value C1 and the second calibrated magnification value C2 are increased or decreased, the first calibrated magnification value C1 or the first calibrated magnification value C1 or The calibration unit 41 can be configured to include a transition process of gradually increasing or decreasing the second calibration magnification value C2 to gradually transition to the calibration completed state.

On the other hand, the stoichiometric amplitude (stoichiometric amplitude (wave height)) of the oxygen sensor 12 changes according to the actual temperature of the sensor element 12a, and the amplitude changes. For example, assuming that the oxygen sensor 12 has a characteristic of a stoichiometric amplitude of 4 volts when the temperature value measured as accurately as possible when new is 600 degC, the sensor heater 12 b undergoes thermal deterioration (oxidation) during the long-term use process. occurs and the resistance value of the sensor heater 12b increases, the temperature of the sensor heater 12b and the temperature T of the sensor element 12a, which are obtained by reading the resistance value of the sensor heater 12b, appear to be the actual values including errors. It shows a value different from the temperature.

For example, if the oxygen sensor 12 has a thermal deterioration of the sensor heater 12b such that the temperature T of the sensor heater 12b read by the heater temperature reading unit 23a based on the resistance value of the sensor heater 12b shows a measured value of 600+50 degC, the characteristic inspection unit 40 , the stoichiometric amplitude characteristic of the oxygen sensor 12 changes along with the actual temperature of the sensor element 12a. , the stoichiometric amplitude will be observed as 4 volts. That is, in this case, the correspondence relationship between the apparent temperature of the sensor heater 12b and the temperature T of the sensor element 12a and the stoichiometric amplitude is shifted by about +50 degC compared to when the sensor heater 12b is new and not thermally deteriorated. Observed.

By checking the deviation from the default correspondence relationship of the data map as described above, the temperature T of the sensor heater 12b obtained by reading from the resistance value of the sensor heater 12b is the actual temperature of the sensor element 12a. It is possible to accurately grasp the degree of temperature error with respect to the value. Further, when the temperature error is large, it can be determined that the sensor heater 12b has deteriorated.

Therefore, in the present embodiment, in order to determine whether or not the sensor heater 12b is degraded, a plurality of excess air ratio values are set to a plurality of first scale values G1 for the temperature T of the sensor heater 12b and a plurality of values for the voltage value VHG. The above-mentioned data map showing correspondence with a plurality of second scale values G2, and the rich side for determining which air-fuel ratio region the voltage value VHG corresponds to: the rich region, the stoichiometric region, or the lean region The above-mentioned lookup table showing the threshold value and the lean side threshold value in correspondence with the first scale value G1 is used.

Also, while reading the wave peak value during operation of the internal combustion engine, the above-described characteristic checking unit 40 checks to which of the air-fuel ratio regions the peak of the read wave peak value corresponds, and based on the result of this check, , and derive the temperature calibration coefficient K (first calibration magnification value C1) for correcting the first scale value G1 and calibrating the above correspondence relationship, the calibration unit 41 described above is used.

Then, when the absolute value of the difference between the initial value and the latest value of the temperature calibration coefficient K is larger than a predetermined deterioration judgment value, the deterioration judgment unit 48 judges that the sensor heater 12b is deteriorated. provided in

The deterioration determination unit 48 acquires the initial value of the temperature calibration coefficient K when the calibration unit 41 performs calibration in the initial stage or when the OBD diagnosis machine, which will be described later, issues a reset command. Each time the latest value of is acquired, the absolute value of the difference between the initial value and the latest value is compared with a predetermined deterioration judgment value, and if the absolute value exceeds the deterioration judgment value, the sensor heater 12b is deteriorated. I judge.

5, the default temperature calibration of the ECU 15, which is set corresponding to the resistance value (median value) of the standard sensor heater 12b, for the temperature calibration coefficient K related to the first scale value G1. A coefficient K value (here, a value that does not change the first scale value G1 from the default, for example, K=1.000) is indicated by line A in FIG. If the temperature calibration coefficient K corresponding to the resistance value of is shown by a line B that deviates from the line A due to manufacturing tolerances (characteristic variations), etc., the temperature correction coefficient K obtained by the deterioration determination unit 48 is set by obtaining the latest value of the temperature calibration factor K fitted to the line B in the calibration section 41 and capturing the latest value. At this time, the deterioration determining unit 48 sets a state flag F indicating whether or not the initial value of the temperature calibration coefficient K, which will be described later, has been set, for example, by a bit (single-digit binary number). is set to "1" indicating that the temperature calibration coefficient K has been changed, thereby prohibiting subsequent changes to the initial value of the temperature calibration coefficient K. Even after the state flag F is set to "1" in this way, the latest value of the temperature calibration coefficient K is updated by the calibration unit 41 as the resistance value or temperature value changes over time due to deterioration of the sensor heater 12b. Therefore, the latest value of the temperature correction coefficient K, in which the updates have been accumulated, deviates from the initial value (line B) of the temperature calibration coefficient K as indicated by lines C and D in FIG. 5, for example. become. Then, the deterioration determining unit 48 determines that the difference between the initial value of the temperature calibration coefficient K related to the first scale value G1 indicated by the line B and the latest value of the temperature calibration coefficient K indicated by the line C or D is the above deterioration. If the distance exceeds the determination value, it can be determined that the sensor heater 12b has deteriorated.

For example, if the deterioration determination value is 0.3, the initial value of the temperature calibration coefficient K for the line B is 1.02, and the latest value of the temperature calibration coefficient K for the line C is 0.935, the temperature The difference between the initial value and the latest value of the calibration coefficient K is 0.085, which in this case is smaller than the deterioration determination threshold value of 0.3, so it is determined that there is no deterioration. Also, for example, if the deterioration determination value is 0.3, the initial value of the temperature calibration coefficient K for the line B is 1.03, and the latest value of the temperature calibration coefficient K for the line D is 1.35 , the difference between the initial value and the latest value of the temperature calibration coefficient K is 0.32. In this case, it is determined that the sensor heater 12b is deteriorated because it is larger than the deterioration determination threshold value of 0.3.

Here, the deterioration determination unit 48 includes a flag storage unit 49 that stores the state flag F in order to set the initial value of the temperature calibration coefficient K appropriately. The flag storage unit 49 is formed of, for example, a rewritable non-volatile memory capable of holding data without power supply to the storage unit. When the state flag F stored in the flag storage unit 49 is "0 (zero)" indicating that the initial value of the temperature calibration coefficient K has not been set, the initial value of the temperature calibration coefficient K is set to the temperature calibration coefficient K , and if the status flag F is "1" indicating that the initial value of the temperature calibration coefficient K has been set, the initial value of the temperature calibration coefficient K is prohibited from being changed. .

As a result, when the state flag F is "0 (zero)" indicating that the initial value of the temperature calibration coefficient K has not been set, the deterioration determination unit 48 determines the initial value of the temperature calibration coefficient K and the temperature calibration coefficient An initial value for the temperature calibration factor K can be set because the most recent value of K is set to the same value (zero difference). That is, it functions as a so-called initializer for the temperature calibration coefficient K, and the initial value of the temperature calibration coefficient K is appropriately set from the latest value of the temperature calibration coefficient K calibrated by the calibration unit 41 .

Further, when the deterioration determination unit 48 determines that the initial value of the temperature calibration coefficient K has been obtained properly based on the result of the inspection by the characteristic inspection unit 40, the deterioration determination unit 48 sets the state flag F to Set to a value indicating that it has been set.

The calibration in the calibration unit 41 is not so-called one-shot learning based on instantaneous observation, but integrally performed by repeatedly increasing and decreasing the gradually derived temperature calibration coefficient K as described above. When it is determined that the latest value of the temperature calibration coefficient K has reached a saturated state and has been properly acquired (calibration has been completed), the deterioration determining unit 48 sets the state flag F to the ON state of "1 ” to prohibit subsequent changes to the initial value of the temperature calibration coefficient K. As a result, the initial value of the temperature calibration coefficient K derived by the deterioration determination unit 48 is a value with excellent reproducibility.

Note that the latest value of the temperature calibration coefficient K, the initial value of the temperature calibration coefficient K, and the state flag F may be rewritten to desired values by commands from an external terminal device. In this case, it is preferable that the temperature calibration coefficient K and the state flag F are rewritten by an operation via an OBD diagnostic machine as an external terminal device.

For example, when the oxygen sensor 12 is replaced with a new one from a deteriorated one during maintenance of an automobile in the process of use, an OBD diagnosis machine is operated to activate the learning value reset command of the ECU 15, and the latest value of the temperature calibration coefficient K and the initial value It is necessary to cancel the determination by the deterioration determination unit 48 that the sensor heater 12b is deteriorated by initializing each parameter such as the value and the state flag F. In order to provide the operation function to do this, the ECU 15 can cooperate with an external terminal device.

However, in this case, the wave height (fluctuation) of the voltage value VHG from the sensor element 12a changes according to the actual temperature (real value) of the sensor element 12a. When checking whether or not the correspondence relationship between the read wave height and the temperature T of the sensor element 12a obtained by reading from the resistance value of the sensor heater 12b conforms to the above data map, the characteristic checking unit 40 checks whether the sensor It is necessary to control the temperature of the heater 12b to an appropriate temperature. That is, if the temperature of the sensor heater 12b is too cold or too hot, proper inspection cannot be performed.

Therefore, in the present embodiment, the ECU 15 further includes a heater control temperature deriving section that obtains the temperature Tc for controlling the heater heat generation control section 22 by multiplying the temperature T of the sensor element 12a by the reciprocal of the temperature calibration coefficient K. 50 is provided, and the heater heat generation control unit 22 causes the sensor heater 12b to generate heat so that the temperature Tc becomes the target temperature Ttrg.

If the latest value of the temperature calibration coefficient K is Kn and the temperature T of the sensor element 12a is Tn, the heater control temperature derivation unit 50 obtains the temperature Tc for controlling the sensor heater 12b by the following equation.
Tc=Tn×(#1/Kn)

The heater heat generation control unit 22 applies a voltage pulse width modulated according to the difference between this temperature Tc and the target temperature Ttrg to cause the sensor heater 12b to generate heat.

As a result, the inspection by the characteristic inspection unit 40 is properly performed, and thus the presence or absence of deterioration of the sensor heater 12b is properly determined. In this case, the target temperature value Ttrg is not limited to a constant value, and may be set so as to vibrate in conjunction with the calibrating unit 41 . That is, the temperature calibration coefficient K can be derived by learning at multiple points while changing the temperature conditions.

As described above, according to the present embodiment, when the absolute value of the difference between the initial value of the temperature calibration coefficient K and the latest value of the temperature calibration coefficient K obtained by the calibration unit 41 is greater than the predetermined deterioration determination value is provided with a deterioration judgment unit 48 for judging that the sensor heater 12b is deteriorated. An additional temperature sensor for measuring the actual temperature of the sensor heater 12b may not be required.

In addition, since it is possible to determine whether or not the sensor heater 12b has deteriorated by interlocking with the calibration unit 41 while the internal combustion engine is operating, it is possible to avoid the conventional inconvenience of having to wait for a long time until the timing at which deterioration can be determined comes. be able to. Therefore, it is possible to provide a control device for an internal combustion engine that can determine the presence or absence of deterioration of the sensor heater 12b at low cost and with few operational restrictions.

Further, when the state flag F indicates that the initial value of the temperature calibration coefficient K has not been set, the deterioration determination unit 48 sets the initial value of the temperature calibration coefficient K to the same value as the latest value, and the state When the flag F indicates that the initial value of the temperature calibration coefficient K has been set, subsequent changes to the initial value of the temperature calibration coefficient K are prohibited. The value allows to set the initial value of the temperature calibration factor K.

Further, when the deterioration determination unit 48 determines that the initial value of the temperature calibration coefficient K has been properly acquired, the state flag F of the flag storage unit 49, which is a nonvolatile memory, is set to "1" (on state). Therefore, after it is determined that the latest value of the temperature calibration coefficient K has reached a saturated state and the state of the heater section has been appropriately captured, the state flag F can be continuously held in the ON state. Also, the properly obtained initial value of the temperature calibration coefficient K can be maintained at a value with excellent reproducibility.

In addition, the deterioration determination unit 48 can rewrite the latest value of the temperature calibration coefficient K, the initial value of the temperature calibration coefficient K, and the state flag F to desired values in response to a command from an external terminal device. When the deteriorated oxygen sensor 12 is replaced with a new one during maintenance of an automobile in use, it is found that the sensor heater 12b in use is deteriorated through an operation via an OBD diagnosis device as an external terminal device. Judgment etc. can be canceled.

Further, the sensor heater 12b is caused to generate heat by the heater heat generation control unit 22 according to the difference between the temperature Tc obtained by the heater control temperature deriving unit 50 and the target temperature Ttrg. The inspection by the unit 40 can be performed appropriately, and the presence or absence of deterioration of the sensor heater 12b can be determined appropriately.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various design changes may be made without departing from the scope of the present invention described in the claims. is possible.

For example, in the above-described embodiment, the data map and the lookup table are substantially transformed in the manner of so-called affine transformation by multiplying the plurality of first scale values G1 of the data map and the lookup table by the first calibration magnification value C1. Although the calibration is performed by expanding or contracting the image (equation (6a)), the present invention is not limited to this. For example, the data map and lookup table can be substantially enlarged or reduced even with a configuration in which the temperature for control for scanning the data map and lookup table is multiplied by the first calibrated magnification value C1. When the value before calibration of the plurality of first scale values G1 stored in the storage unit 34 is Tk (degrees Celsius), and the first scale value for control after calibration is Tkcal, the data map and lookup A temperature value Tcon (temperature in degrees Celsius) for scanning control for scanning the table can be obtained by the following equation (6b).
Tkcal = Tk
Tcon = (T + TD + 273.15) x (1/C1) - 273.15
(6b)

In the configuration using either the above formula (6a) or formula (6b), the peak value of the actually measured voltage value (detection value) VHGcon matches the rich side and lean side thresholds (the peak of the wave height is It is possible to calibrate so that it overlaps with the threshold value), calculate an accurate excess air ratio, and perform appropriate air-fuel ratio feedback control. Further, it is possible to appropriately determine whether or not the sensor heater 12b is deteriorated while appropriately performing inspection by the characteristic inspection unit 40. FIG.

In the above-described embodiment, the reference value Tref for setting the temperature Tcon is obtained by adding the intake air temperature obtained by the intake air temperature sensor 8 to the engine temperature obtained by the cooling water temperature sensor 17 and dividing by 2 {Tref= (engine temperature + intake air temperature) ÷ 2}, but not limited to this, for example, either the engine temperature obtained by the cooling water temperature sensor 17 or the intake air temperature obtained by the intake air temperature sensor 8 The reference value Tref for setting the temperature Tcon may be calculated from only one.

1: engine body, 2: intake pipe, 3: throttle valve, 4: air cleaner, 5: throttle sensor, 6: fuel injection valve, 7: intake pressure sensor, 8: intake temperature sensor, 9: piston, 10: exhaust pipe 11: Catalyst 12: Oxygen Sensor 12a: Sensor Element (Detector) 12b: Sensor Heater 13: Spark Plug 14: Ignition Device 15: ECU (Electronic Control Unit) 17: Cooling Water Temperature Sensor 18 : Crankshaft 19: Crank angle sensor 19a: Rotor 19b: Pickup 20: Atmospheric pressure sensor 22: Heater heat generation control unit 23: Temperature calculation unit 23a: Heater temperature reading unit 23b: Detecting unit temperature estimation 24: Voltage calculator 25: Excess rate calculator 26: Alternative value calculator 27: Rotational speed calculator 28: Target value calculator 29: Basic injection amount calculator 30: Feedback coefficient calculator , 31: injection amount calculation unit, 32: torque calculation unit, 33: limit threshold value setting unit, 34: storage unit, 35 to 38, 35b, 36b, 35c, 36c, 35d, 36d, 35e, 36e: graph, 40: Characteristic inspection unit 41: Calibration unit 42: Temperature difference confirmation unit 43: Voltage difference confirmation unit 44: Voltage waveform 45: Air-fuel ratio waveform 46: Rich side peak 47: Lean side peak 46v, 47v: peak value, 48: deterioration determination unit, 49: flag storage unit, 50: heater control temperature derivation unit.

Claims (5)

1. A detector provided so as to be in contact with exhaust gas from an internal combustion engine having exhaust pulsation, the resistance value of which changes stepwise at an oxygen concentration in the vicinity of the stoichiometric exhaust gas, and a heater part adjacent to the detector. a high-temperature exhaust gas oxygen sensor having a pulse waveform in which a detection value obtained from the resistance value of the detection portion exhibits a pulse waveform having a crest value corresponding to the temperature of the detection portion and the exhaust pulsation;
   a heater temperature reading unit that obtains the temperature of the heater unit based on the resistance value of the heater unit;
   a detector temperature estimator that obtains the temperature of the detector based on the temperature of the heater;
   A data map showing a plurality of excess air ratio values in correspondence with a plurality of first scaled values for the temperature of the detection unit and a plurality of second scaled values for the detected value, and a data map showing the detected value is rich. A memory for storing a lookup table showing a rich side threshold value and a lean side threshold value for determining which air-fuel ratio region of the region, the stoichiometric region, or the lean region corresponds to the first scale value. A control device for an internal combustion engine comprising:
   a characteristic inspection unit for inspecting which of the air-fuel ratio regions the peak of the read wave height value corresponds to while reading the wave height value during operation of the internal combustion engine;
   a calibration unit that derives a temperature calibration coefficient for correcting the first scale value and calibrating the correspondence relationship based on the result of the inspection;
   and a deterioration determination unit that determines that the heater unit has deteriorated when the absolute value of the difference between the initial value and the latest value of the temperature calibration coefficient is larger than a predetermined deterioration determination value. A control device for an internal combustion engine.
2. The deterioration determination unit includes a flag storage unit that stores a state flag indicating whether or not the initial value of the temperature calibration coefficient has been set,
   if the status flag indicates that the initial value of the temperature calibration factor has not been set, setting the initial value of the temperature calibration factor to the same value as the latest value of the temperature calibration factor;
   2. A control apparatus for an internal combustion engine according to claim 1, wherein when said status flag indicates that said initial value of said temperature calibration coefficient has been set, said initial value of said temperature calibration coefficient is prohibited from being changed. .
3. The deterioration determination unit sets the state flag of the flag storage unit to the initial value of the temperature calibration coefficient when it is determined that the initial value of the temperature calibration coefficient has been properly acquired based on the result of the inspection by the characteristic inspection unit. 3. The control device for an internal combustion engine according to claim 2, wherein a value indicating that the value has been set is set.
4. 3. The internal combustion engine according to claim 2, wherein the latest value of the temperature calibration coefficient, the initial value of the temperature calibration coefficient, and the state flag can be rewritten to desired values by a command from an external terminal device. Engine control device.
5. a heater control temperature derivation unit that obtains a heater control temperature Tc by the following equation, where K is the latest value of the temperature calibration coefficient and T is the temperature of the detection unit;
   Tc=T×(#1/K)
   2. A heater heat generation control section for applying a voltage pulse-width-modulated according to a difference between the temperature Tc for heater control and a predetermined target temperature Ttrg to cause the heater section to generate heat. A control device for an internal combustion engine according to .

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